Doctor Who and the Pescatons was the first original, officially licensed audio drama based upon Doctor Who. Originally released by Argo Records, the story featured Tom Baker and Elisabeth Sladen, as the Fourth Doctor and Sarah Jane Smith. It was divided into two episodes, complete with opening and closing themes, simulating the televised series.

Discounting a couple of radio appearances and an LP version of Genesis of the Daleks with added narration, The Pescatons was the last time that Baker participated in an original Doctor Who audio drama until the Hornets' Nest arc in 2009.

Who or what is the mighty Zor, whose green slanting luminous eyes glare out from the dark of night like giant emeralds? What is the powerful alien force that is bringing Earth's civilisation to a standstill, threatening to annihilate everything in its path?

This is the story of a dying Planet, of a Deadly Weed, and the merciless Creatures themselves. It is a Challenge to the Doctor—a frightening race against time...

The TARDIS arrives on a beach by the Thames Estuary at night, and the Doctor and Sarah Jane discover a metallic seaweed there.

The Doctor consults with Professor Emerson, who says that three expeditions to recover a recent meteorite from the bottom of the estuary have all vanished. The Doctor goes diving and is nearly killed by something that wraps itself around him, but then lets him go. He discovers that the meteorite is a wrecked spaceship buried under the estuary, and he knows where it comes from

The Doctor tells Sarah Jane about the Pescatons, a form of carcharhinidae, or deep water shark. Naturally, the experts scoff until one comes out of the Thames and makes its way to London Zoo in search of salt water. The Doctor confronts it in the Aquarium, where it dies and disintegrates.

That night, more meteorites land in the Thames.

Part two

London is invaded, and the Doctor recalls his visit to planet Pesca, home of the Pescatons. He fell down a chasm into a cavern and met Zor, the leader of the Pescatons who informed him that they were going to use him to find a new home now that their own planet was drying out as it fell towards their sun. Zor used his hypnotic powers on the Doctor, who fought back and escaped.

Back in London, Sarah Jane finds an abandoned baby while the military try to shoot the invading Pescatons to no avail. The Doctor distracts a Pescaton by singing Hello Dolly and doing a dance so that Sarah Jane can get away with the child. Finally the Pescatons retreated back into salt water, except for one trapped in an Underground tunnel. The Doctor and Sarah Jane go in search of it, and the Doctor starts playing his piccolo to calm his nerves. The Pescaton retreats at the sound.

Professor Emerson helps the Doctor build a high frequency sound trap inside a sewer, and Zor is lured there to be destroyed as the planet Pesca disintegrates in its orbit. Without Zor to control it, the Pescaton invasion ends.

Unusually, the Doctor here calls the Pescatons "evil" on many occasions. This characterisation of another species is atypical for the Doctor. Indeed, it lays the foundation for another extraordinary feature of the story: the Doctor and Sarah devise and participate in the remorseless genocide of the Pescatons.

A scene which once may have played as a "Tom Baker-ism" now has retroactive continuity with A Good Man Goes to War and Closing Time. At one point, the Doctor and Sarah Jane encounter an abandoned baby on the streets of London. The Doctor attempts to talk to him, but flatly says that "he won't talk." Sarah corrects him, saying that "he can't talk." Since modern listeners know that the Eleventh Doctor claims to be able to speak "Baby," the scene now plays as though the Doctor's statement is probably more accurate than Sarah's.